1. Technical Field
The invention relates to hand-held instruments and to their production. Examples of such instruments include moisture meters, thermometers, pH meters, and humidity meters.
2. Prior Art Discussion
At present, many such instruments comprise a moulded plastics housing within which is inserted the necessary circuits and input and output devices. The housing often comprises two moulded plastics halves which are either screwed or clipped together.
One problem with such a construction is that production of the instrument is expensive because production steps are relatively awkward and difficult to automate, and because there are a relatively large number of parts. For example, it is awkward to insert a circuit and the relevant components into the housing halves and to secure them into position. Another production problem is that in many cases each different type of instrument within a range of instruments must be produced individually from the beginning of the production process, because different housings will often be required for each circuit. There is thus very little versatility in production.
One attempt at improving production efficiency for instruments generally is described in British Patent Specification No. 1183647 (DE'ATH). This specification describes an instrument case comprising a front, a back and four side plates, which are all screwed together at mitred corners. Because the individual plates may be extruded and cut to the desired length, it appears that production efficiency would be improved in comparison with the first-mentioned prior art. However, this instrument has quite a large number of parts and thus production efficiency and cost would appear to be still quite high.
A further problem with presently available hand-held instruments is that the housing or casing may be relatively easily distorted. This can cause considerable problems for instruments such as moisture meters where it is essential that the support for sensors such as capacitive pads remain rigid.